Polyamine conjugates with acidic retinoids and preparation thereof

ABSTRACT

Invented are novel polyamine conjugates which have been readily obtained using as key-step the condensation of linear, conformationally restricted, cyclic and branched polyamines or suitably protected derivatives with vitamin A derivatives. These compounds inhibit the ribozyme ribonuclease P (RNase P) and the production of interleukin-2 (IL-2) and interferon-γ (INF-γ) by peripheral blood mononuclear cells in vitro.

FIELD OF THE INVENTION

This invention relates to the preparation of a series of novel polyamine conjugates with vitamin A derivatives which inhibit the ribozyme RNase P and the production of IL-2 and IFN-γ by peripheral blood mononuclear cells in vitro and have potential therapeutic applications in neoplastic, keratinization and inflammatory disorders. In particular, the invention relates to conjugates, obtained from the condensation of linear, conformationally restricted, cyclic and branched polyamines with acidic retinoids, such as all-trans-retinoic acid.

BACKGROUND OF THE INVENTION

Linear polyamines, like spermine (SPM, 1) and spermidine (SPD, 2), and their compounds with other natural products, collectively coined as polyamine conjugates, are widely distributed in living organisms and exhibit interesting biological properties.

In order to determine structure-biological activity relationships and possibly identify lead compounds for the development of polyamine-based pharmaceuticals, a variety of linear, branched, conformationally restricted and cyclic polyamine analogues and conjugates have been synthesized (Blagbrough et al., PHARM. SCI., 3, 223 (1997); Schulz et al., ANGEW. CHEM. INT. END. ENGL., 36, 314 (1997); Papaioannou et al., EUR. J. ORG. CHEM., 1841 (2000) and Kong Thoo Lin et al., SYNTHESIS, 1189 (2000)). Due to their polycationic nature, polyamines interact strongly with nucleic acids and play an important role in their biosynthesis and metabolism. They stabilize DNA conformation and can induce conformation changes through the formation of intra- or intermolecular bridges. Polyamines cause specific modifications of specialized RNA molecules, stabilize ribonucleases and stimulate the action of ribonucleases and ribozymes. They exert pleiotropic effects on protein synthesis, are essential for normal growth and involved in the differentiation processes of mammalian cells. The concentrations of polyamines and the enzymes responsible for their biosynthesis are notably higher in rapidly proliferating mammalian cells; generally, these concentrations increase in all cells upon induction of differentiation. Polyamines are directly responsible for the increased rate of the macromolecular synthesis occurring during tumour development and growth. Inhibition of the biosynthetic enzymes producing polyamines and of the polyamine uptake system responsible for feeding the cell with exogenous polyamines have emerged as very attractive targets for cancer chemotherapy. Recently, selectively N-alkylated polyamines which partially mimic natural polyamine behaviour, inhibit cell growth and are metabolically stable have been developed as novel anticancer agents (for leading references see the review by Papaioannou et al., EUR. J. ORG. CHEM., 1841 (2000)).

The retinoids constitute a large family of organic compounds structurally related to the naturally occurring Vitamin A (retinol, 3) and analogues, such as retinal (4) and all-trans-retinoic acid (5) and a variety of other synthetic analogues, such as acitretin (6), 13-cis-retinoic acid (7) and 9-cis-retinoic acid (8). The polyene chain-shortened all-trans-retinoic acid analogues 9 and 10 may be also considered as members of this family.

Retinoids can cause specific biological responses upon binding to and activating special receptors or groups of receptors. Natural and synthetic retinoids play an important role in vision, cell growth, reproduction, proliferation and differentiation of various epithelial or non-epithelial tissues. Although they are already widely used in systemic and topical treatment of various disorders, retinoids reveal a considerable number of side-effects even when used in therapeutic doses. Thus, numerous new retinoid analogues have been synthesized in an attempt to improve the therapeutic index, biological profile and selectivity of these compounds for clinical application in dermatology, oncology, rheumatology and immunology (for general monographies see Sporn, Roberts and Goodman (Eds.), The Retinoids, vol. 1 and 2, Academic Press, Orlando, 1984; Sporn and Roberts, CIBA FOUND. SYMP., 113, 1 (1985); Sporn, Roberts and Goodman (Eds.), The Retinoids: Biology, Chemistry and Medicine, 2^(nd) ed., Raven Press, New York, 1994; Dawson and Okimura (Eds.), Chemistry and Biology of Synthetic Retinoids, CRC Press, Boca Raton, 1990; Packer (Ed.), Methods in Enzymology, Academic Press, vol. 189, part A, 1990 and vol. 190, part B, 1991)). The clinical application of synthetic retinoids in the management of recalcitrant and previously incurable neoplastic, inflammatory and keratinization disorders has introduced a real revolution in dermatology and other medical fields (Tsambaos, DERMATOSEN, 44, 182 (1996), Muindi, CANCER TREAT. RES., 87, 305 (1996)). By regulating gene expression, retinoids are capable of regulating the differentiation and growth of transformed cells or of inhibiting the malignant transformation of a variety of cells reversing their differentiation (DeLuca, FASEB J., 5, 2924 (1991), Lotan and Glifford, BIOMED. PARMACOTHER., 45, 145 (1991)). In the mechanisms of regulation of gene expression by retinoids certain members of the large family of steroid and thyroid gland hormones receptors are involved, that is nuclear proteins to which retinoids specifically bind (DeLuca, FASEB J., 5, 2924 (1991), Leid et al., TRENDS BIOCHEM. SCI., 17, 427 (1992)). Retinoid receptors have been already isolated and studied (Redfern, PATHOBIOL. 60, 254 (1992), Giguere et al., NATURE, 330, 624 (1987), Petkovich et al., NATURE, 330, 444 (1987)). They act as transcription factors following activation by suitable ligands. Currently, the development of new retinoid-based drugs is based on the synthesis of novel ligands for the retinoic acid receptors RARα,β,γ and RXRα,β,γ and the orphan receptors (Lippman and Lotan, J. NUTR. 130(2S Suppl), 479S (2000)).

It has been recently reported that natural retinoids, like retinoic acid and retinol, as well as synthetic analogues of retinoic acid, e.g. isotretinoin (13-cis-retinoic acid), acitretin and the arotinoids Ro 13-7410, Ro 15-0778, Ro 15-1570 and Ro 13-6298 but also other compounds, e.g. calcipotriol, anthralin and their combination, known for their antipsoriatic activity, inhibit the enzyme ribonuclease P (RNase P) (Papadimou et al., J. BIOL. CHEM. 273, 24375 (1998), Papadimou et al., SKIN PHARMACOL. APPL. SKIN PHYSIOL. 13, 345 (2000), Papadimou et al., EUR. J. BIOCHEM. 267, 1173 (2000), Drainas et al., SKIN PHARMACOL. APPL. SKIN PHYSIOL.13, 128 (2000), Papadimou et al., BIOCHEM. PHARMACOL. 60, 91 (2000)), which has been isolated and characterized from the slime mold Dictyostelium discoideum (Stathopoulos et al.; EUR.J. BIOCHEM. 228, 976 (1995)) and from normal human epidermal keratinocytes.(Drainas et al, unpublished results). These finding advocate the hypothesis that retinoids, in addition to regulating DNA transcription, can also regulate the activity of enzymes playing key-roles in macromolecular biosynthesis, by their implication in post-transcriptional processes, in which binding to the retinoic acid receptors is not involved. RNase P is responsible for the ripening of the 5′ terminus of precursor tRNA molecules. RNase P activity have been found in all pro- and eucaryotic organisms studied so far (Frank and Pace ANNU. REV. BIOCHEM. 67, 153 (1998)). RNase P enzymes are complexes of RNA with proteins and their activity is mainly attributed to their RNA subunit. Several findings indicate that the structure of the RNA subunit is of similar size in pro- and eucaryotic organisms and that the structures of RNase P from different eucaryotic organisms are similar. For these reasons, it appears that RNase P from D. discoideum and human epidermal keratinocytes are good models for the identification and development of new inhibitors.

SYNOPSIS OF INVENTION

Attaching a polyamine on another bioorganic molecule results in the formation of a polyamine conjugate. Depending on the structure of the non-polyamine moiety, these conjugates are designed to exhibit improved biological activity on particular cellular targets or combine the activities of the constituent molecules. The compounds (conjugates) of the present invention were synthesized in an attempt to combine the biological profiles of polyamines and retinoids. They were all obtained by using as key-step the coupling of the polyamine analogues tabulated in FIG. 1 with the retinoids depicted in FIG. 2. It was anticipated that the polyamine affinity for nucleic acids, e.g. the RNA part of RNase P, would enforce the binding of natural and synthetic retinoids on the same molecule. Recently, N¹, N³-diretinoyl-1,3-diaminopropane was synthesized, from 1,3-diaminopropane and retinoyl chloride, as potential antitumour agent but showed low cytostatic activity (Manfredini et al., J. MED. CHEM., 40, 3851 (1997)), whereas cosmetic and/or dermatological compositions consisted of retinol or retinol esters and polyamine polymers were prepared and showed that the polyamine polymers provide superior stabilization to retinol in skin care compositions compared to known products with antioxidant or retinol stabilizing properties (Nguyen et al, U.S. Pat. No. 6,344,206 B1).

Indeed, the conjugates described in the present invention reveal stronger inhibitory effects on RNase P isolated from D. discoideum and human epidermal keratinocytes than the parent retinoids or a combination of free polyamines and the corresponding retinoids (Table 1). From the same studies it appears that the more free amino functions in the conjugates are available to interact, the stronger is the RNase P inhibition (e.g. the spermine conjugate with all-trans-retinoic acid is a stronger inhibitor than the corresponding spermidine conjugate). On the other hand, conjugates with two retinoid residues are more active than those with one residue (e.g. spermine bearing two all-trans-retinoic acid residues is a stronger inhibitor than spermine bearing only one). In addition, these compounds show an inhibitory effect on the production of IL-2 and IFN-γ by peripheral blood mononuclear cells of healthy human subjects in vitro. In sharp contrast, the currently available retinoids show a stimulatory effect on the production of these cytokines. These results indicate that the compounds described herein have significant potential for clinical application in the treatment of neoplastic, inflammatory and keratinization disorders.

DESCRIPTION OF DRAWINGS

FIG. 1: Structures of polyamines used to prepare the conjugates described in the present invention

FIG. 2 : Structures of retinoids used to prepare the conjugates described in the present invention

FIG. 3 : General method for the preparation of isolable succinimidyl esters of acidic retinoids

FIG. 4 : Synthetic schemes for the preparation of N^(α)-mono- and N^(α), N^(ω)-bisamides of linear polyamines with acidic retinoids

FIG. 5 : Synthetic schemes for the preparation of the N⁴,N⁹-bisamide of spermine and of all three N-monoamides of spermidine with acidic retinoids

FIG. 6 : Synthetic schemes for the preparation of N^(α),M^(ω)-bisamides of conformationally restricted tetra- and hexa-amines with acidic retinoids

FIG. 7 : Synthetic schemes for the preparation of polyamides symmetric and asymmetric dimers of spermine and spermidine and of cyclic hexa- and octa-amines and of with acidic retinoids

FIG. 8 : Double reciprocal plot (1/v versus 1/[pre-tRNA]) for RNase P reaction in the presence of N¹,N¹²-RA₂-Spermine. The reaction was carried out at the indicated concentrations in the presence or absence of inhibitor. All reactions were carried out at 37° C. in 20 μl buffer D in the presence of 10% DMSO. (♦) without inhibitor, with N¹, N¹²-RA₂-Spermine at (▪) 3 μM, (▴) 4 μM, (●) 5 μM. Top panel: Replot of the slopes of the double reciprocal lines versus inhibitor (I) concentrations.

FIG. 9 : Effect of N¹,N¹²-RA₂-SPM on the percentage of CD4+/IL-2+ and CD8+/IL-2+ peripheral blood mononuclear cells.

FIG. 10: Effect of N¹, N¹²-RA₂-SPM on the mean fluorescence intensity (MFI) of CD4+/IL-2+ and CD8+/IL-2+ peripheral blood mononuclear cells.

FIG. 11: Effect of N¹,N¹²-RA₂-SPM on the percentage of CD8+/IFN-γ+ peripheral blood mononuclear cells.

FIG. 12 : Effect of N¹,N¹²-RA₂-SPM on the mean fluorescence intensity (MFI) of CD8+/IFN-γ+ peripheral blood mononuclear cells.

SUMMARY OF THE INVENTION AND DESCRIPTION OF THE PREFERRED EMBODIMENTS

The compounds of the present invention are polyamine conjugates with acidic retinoids, which are prepared through the condensation of either free polyamines or selectively protected polyamines, from those depicted in FIG. 1, with either the retinoids directly or the corresponding succinimidyl esters of the acidic retinoids tabulated in FIG. 2. The conjugates of the present invention are inhibitors of the enzyme RNase P, isolated from the slime mold D. discoideum and human epidermal keratinocytes. The most potent inhibitor among these conjugates has also shown excellent inhibitory effects on the production of IL-2 and INF-γ by peripheral blood mononuclear cells. Thus, it is reasonable to assume that these compounds may be useful in the management of inflammatory disorders.

The biological evaluation of the conjugates of the present invention through the examination of their inhibitory activity on RNase P from slime mold D. discoideum and human epidermal keratinocytes constitutes a rapid and safe test for evaluation of their potential to modulate the epithelial differentiation and proliferation and to reverse the malignant transformation of epithelial cells. Thus, alternative laborious tests for retinoid screening based on the retinoic acid receptor (RAR) mediated transcriptional activation (Astrom, BIOCHEM. BIOPHYS. RES. COMMUN., 173, 339 (1990)), or suppression of the expression of an enzyme (Michel, ANAL. BIOCHEM., 192, 232 (1991)), or the induction of a protein RNA (Elder, J. IVEST. DERMATOL. 106, 517 (1996)) become unnecessary.

One subfamily of the compounds of the present invention is represented by the following general formulae 3DI-3DIX, which represent conjugates of linear polyamines, of variable numbers of carbon and nitrogen atoms in the chain, with acidic retinoids.

The subscript n in the formula 3DVIII varies from 2-9 and in the formula 3DIX from 1-9. The substituent R is one of the following substituents R¹-R⁶, preferably R¹.

The other subfamily of the compounds of the present invention with the general formulae 3DX-3DXVII, includes conjugates of conformationally restricted, cyclic and branched (dimeric) polyamines with acidic retinoids. Restriction of conformation in the polyamine moiety is imposed by e.g. aromatic rings incorporated in the chain (conjugates 3DX and 3DXI) or heterocyclic rings (conjugates 3DXII) whereas the cyclic polyamines used are of various ring-sizes and contain different numbers of carbon, nitrogen and oxygen atoms in the ring (conjugates 3DXIII-3DXVI). In this subfamily, the polyamine moiety also consists of symmetric or asymmetric polyamine (spermine and spermidine) dimers (conjugates 3DXVII). In this category of compounds, the substituent R is one of the above mentioned, R¹-R⁶preferably R¹, whereas n is one of the numbers 1, 2 and 7. In compounds 3DXVIIA, R′is identical to R″ and equal to COR. In compounds 3DXVIIB, R′ is also identical to R″ but equal to (CH₂)₃NHCOR. Finally, in compounds 3DXVIIC, R′ is equal to COR and R″ is equal to (CH₂)₃NHCOR.

Synthesis

Key-reaction in the synthesis of the polyamine amides described in the present invention is the coupling of an acidic retinoid or activated derivatives of an acidic retinoid with either a free polyamine (direct method) or a suitably protected derivative of a polyamine (indirect method). The acidic retinoids used in this work were either commercially available, e.g. all-trans-retinoic acid (ALDRICH), 9- and13-cis-retinoic acid (SIGMA) and acitretin (ROCHE) or synthesized using standard reactions, e.g. the polyene chain-shortened all-trans-retinoic acid analogues 9 and 10 depicted in FIG. 2. In particular, β-ionylideneacetic acid (9) was obtained according to a published protocol (Tietze und Eicher, ‘Reactionen und Synthesen im organisch-chemischen Praktikum’, Thieme, New York, 1981, p 445), whereas β-ionylidene-trans-crotonic acid (10) was synthesized from β-ionylidenethanol (previous reference, p. 446) through a three-steps protocol involving oxidation to the corresponding aldehyde with o-iodoxybenzoic acid (IBX) in DMSO (Frigerio et al, J. ORG. CHEM., 60, 7272 (1995)), Wittig reaction with diethyl (ethoxycarbonyl)methylphosphonate and finally saponification. Taking into consideration the sensitivity of retinoids towards strongly acidic reagents, we chose to activate the acidic retinoids in the form of their corresponding ‘active’ esters with N-hydroxysuccinimide (HOSu) which are hydrolytically relatively stable and can be readily purified, if necessary, with flash column chromatography (FCC). In addition, the succinimidyl esters of α,β-unsaturated carboxylic acids react only with the primary amino group of polyamines (Papaioannou et al, TETRAHEDRON LETT., 43, 2593 (2002)). The succinimidyl esters of acidic retinoids (21) are simply obtained (FIG. 3) by treating the acidic retinoid with HOSu in the presence of the coupling agent N,N′-dicyclohexylcarbodiimide (DCC) (see EXAMPLE 1). The succinimidyl esters 21 thus obtained are of sufficient purity to be used in the next step. However, pure samples can be readily obtained through purification with FCC. Esters 21 are then used to acylate the primary amino groups of either the free polyamines (direct method) or polyamines protected at their secondary amino functions with protecting groups, such as 9-fluorenylmethoxycarbonyl (Fmoc) or trifluoroacetyl (Tfa), which can be subsequently removed under basic conditions (indirect method). Examples of both methodologies in the preparation of linear N⁶⁰ -mono(3DII)- and N^(α),N^(ω)-diacetylated tetra-amines (3DI and 3DVIII) and N^(α),N^(ω)-diacetylated triamines (3DIV) and hexa-amines (3DIX) are presented in FIG. 4 and detailed under the EXAMPLES 2 and 3. Useful precursors for the indirect methodology are polyamines bearing the triphenylmethyl (trityl, Trt) protecting group at their terminal amino functions, like 22, 26 and 27, whose preparation has been described by one of the inventors using the amide approach for the assembly of the polyamine chain (Papaioannou et al, TETRAHEDRON LETT., 36, 5187 (1995); 39, 5117 (1998); 42, 1579 (2001); 43, 2593 and 2597 (2002) and Papaioannou et al, in ‘Drug Discovery and Design: Medical Aspects’, J. Matsoulkas and T. Mavromoustakos (Eds.), IOS Press, Amsterdam, 2002, in press). These precursors are then routinely protected at their secondary amino function(s) with e.g. the Fmoc group and finally detritylated by a solution of trifluoroacetic acid (TFA) in dichloromethane (DCM). Mono- and/or bisacylation is then performed using one or two equivalents of esters 21, respectively. Finally, secondary amino group deprotection is carried out using a 20% solution of piperidine (Pip) in DCM, following routine purification of the fully protected intermediates by FCC, if necessary.

The preparation of polyamines acylated at their secondary amino functions by activated acidic retinoid derivatives is exemplified in FIG. 5 with the preparation of the spermine conjugates 3DIII and described in detail under the EXAMPLE 4. Thus, selective trifluoroacetylation of the primary amino functions (O'Sullivan and Dalrympe, TETRAHEDRON LETT., 36, 3451 (1995); Blacklock et al, TETRAHEDRON LETT., 36, 7357 (1995); Krakowiak and Bradshaw, SYNTH. COMMUN., 28, 3451 (1998); Blagbrough et al, TETRAHEDRON, 56, 3439 (2000)) with CF₃CO₂Et followed by acylation of the remaining amino functions with the acidic retinoid in the presence of the powerful coupling agent bromotripyrrolidinophosphonium hexafluorophosphate (PyBrOP) and ^(i)Pr₂NEt leads to the fully protected spermine derivatives 28, from which the projected conjugates 3DIII are obtained through alkaline hydrolysis. Using the same methodology described in detail under and EXAMPLE 5, the N⁴-monoacylated spermidine conjugates 3DVI were obtained (FIG. 5), whereas the other two possible regioisomers 3DV and 3DVII became available through the corresponding N¹(29)- and N⁸(30)-tritylspermidines, according to the methodology also described in FIG. 5 and detailed under the EXAMPLE 6. The preparation of the former precursor has been already described (Papaioannou et al, TETRAHEDRON LETT., 42, 1579 (2001)) whereas the latter was readily obtained through coupling of the chloride Fmoc-NH(CH₂)₂COCl (Papaioannou et al, TETRAHEDRON LETT., 36, 5187 (1995)) with N-tritylputrescine in the presence of ^(i)Pr₂NEt, followed by routine removal of Fmoc group and finally LiAlH₄-mediated reduction.

The preparation of the polyamine bisamides 3DX-3DXIV incorporating two retinoid residues at their primary amino functions is described in FIG. 6 and is identical to the direct preparation of the conjugates 3DVIII.2SuOH (FIG. 4). It involves simple treatment of the tetra-amines 13-15 and 18 and the hexa-amine 16 with two molar equivalents of the succinimidyl esters 21. In case the free bases are not readily available, the corresponding polytrifluoroacetate salts are used instead and ^(i)Pr₂NEt for their in situ neutralization (see EXAMPLE 2, direct method B). Syntheses of the polyamines 13-16 and 18, used as starting materials in these preparation, have been already described by one of the inventors (Papaioannou et al, TETRAHEDRON LETT., 43, 2593 (2002) and Papaioannou et al, in ‘Drug Discovery and Design: Medical Aspects’, J. Matsoulkas and T. Mavromoustakos (Eds.), IOS Press, Amsterdam, 2002,. in press). Finally, the preparation of the polyamine tri(3DXV)- and tetra(3DXVI and 3DXVIIA-C)-amides incorporating three and four retinoid residues, respectively, at their primary amino functions is described in FIG. 7. These syntheses involve the coupling of the corresponding polyamines 19 and 17 and 20 with three and four molar equivalents, respectively, of succinimidyl esters 21. The synthesis of polyamines 17 (Papaioannou et al, TETRAHEDRON LETT., 43, 2597 (2002)) and 19 and 20 (Papaioannou et al, TETRAHEDRON LETT., 43, 2593 (2002)) has been also recently described.

Biological Evaluation

Inhibitory Activity on RNAse P. We have developed a method by which we can estimate rapidly the biological activity of the polyamine-retinoid conjugates. This method is based on the effect of the polyamine-retinoid conjugates on RNase P activity and is described in detail under the EXAMPLE 7. All synthesized conjugates were screened for their effect on RNase P activity by constructing the dose response curves. From the dose response curves the IC₅₀ value (the concentration of conjugate at which the product formation is reduced by 50%) is calculated (Papadimou et al., J. BIOL. CHEM. 273, 24375 (1998)), which is a first and quite reliable measure for the potency of retinoid analogues. The accurate estimation of the inhibitory potency on the RNAse P of the strongest polyamine-retinoid conjugates were elucidated by detailed kinetic analysis of their effect on D. discoideum or human epidermal keratinocytes RNase P activity. In order to carry out such analysis, the initial velocity in the presence or absence of the conjugate was determined from the initial slopes of time plots. The data plotted in double reciprocal plots (1/v versus 1/[S]) with increasing concentrations of polyamine-retinoid conjugates and the K_(i) values (the dissociation constant of the inhibitor (I), where I is a polyamine-retinoid conjugate, with the enzyme) were determined from the replots of the slopes of the double reciprocal plots versus the inhibitor's concentration (Papadimou et al., J. BIOL. CHEM. 273, 24375 (1998), Papadimou et al., SKIN PHARMACOL. APPL. SKIN PHYSIOL. 13, 345 (2000)). These replots lead to the graphical determination of K_(i) values from the negative intercept of the line with the I-axis. FIG. 8 shows the double reciprocal plot and the slope replot for N¹,N¹²-bisretinoylspermine. Similar plots were constructed for all conjugates. The K_(i) value is a very good measure for the accurate potency of the polyamine-retinoid conjugates. The K_(i) values of the effect of the most potent polyamine-retinoid conjugates on D. discoideum RNase P activity are presented in Table 1, below, in comparison to known natural and synthetic retinoids and arotinoids. Similar K_(i) values were obtained with normal human epidermal keratinocytes RNase P.

Anti-Inflammatory Activity. Preliminary experiments were performed to determine the optimum conditions for IL-2 and IFN-γ detection intracellularly (data not shown), which mainly involved determination of brefeldin, ionomycin and PMA concentrations and duration of the incubation period and of the brefeldin presence. It was determined that the addition at the initiation of the incubation period of 5 ng/ml of PMA in combination with 250 ng/ml of ionomycin, as well as the addition for the last 2 h of a 4 h incubation period of 5 μg/ml of brefeldin, were accompanied by a peak release of both cytokines in the intracellular space.

PBMC incubation in the presence of PMA/ionomycin was accompanied in all experiments by a significant up-regulation of the IL-2 and IFN-γ expression compared to the unstimulated cultures. This was manifested on both CD4+ and CD8+ lymphocytes and was evidenced both as an up-regulation of the lymphocyte percentage, as well as an upregulation of the fluorescence intensity. Furthermore, it was observed that CD4+ lymphocytes were the major producers of IL-2, whereas CD8+ lymphocytes were mostly producing IFN-γ.

Addition of a polyamine-retinoid conjugate, e.g. N¹,N¹²-RA₂-SPM, at the initiation of the culture, at concentrations 10⁻⁴, 10⁻⁵ and 10⁻⁶ M, had a variable effect on PMA/ionomycin-induced IL-2 levels (see EXAMPLE 8). The highest concentration of the conjugate (10⁻⁴ M) caused a decrease in the percentage of CD4+/IL-2+ and CD8+/IL-2+ cells, as well as in the intensity of fluorescence, whereas the other two concentrations had a minimal or no effect. At a concentration of 10⁻⁴ M, the polyamine-retinoid conjugate induced a decrease in CD4+/IFN-γ+ cell intensity of fluorescence and percentage of CD8+/IFN-γ+ cells, whereas the other two lower concentrations revealed a minimal or no effect (FIGS. 9-12)

TABLE 1 Selected equilibrium constants derived from primary and secondary plots. K_(i) ^(a) Polyamine conjugates with retinoids K_(i) ^(a) Retinoids (μM) (new compounds) (μM) Retinol 1,475 N¹-RA-Spermine (3DIIa) 2.4 all-trans-Retinoic 15 N¹,N¹²-RA₂-Spermine (3DIa) 0.5 acid (RA) Isotretinoin 20 N⁴,N⁹-RA₂-Spermine (3DIIIa) 1.1 Acitretin (Aci) 8 N¹-Aci-Spermine (3DIIb). 3 HCl 2.45 Ro 13-7410 45 N¹,N¹²-Aci₂-Spermine (3DIb). 2 HCl 0.95 Ro 15-0788 2,800 Ro 15-1570 3,600 Ro 13-6298 4,350 RA + Spermine 15 ^(a)The K_(i) values are calculated from the negative intercept of the slope replots (see FIG. 8)

EXAMPLES Experimental

Capillary melting points were taken on a Büchi SMP-20 apparatus and are uncorrected. IR spectra were recorded as KBr pellets or with neat oily samples on a Perlkin-Elmer 16PC FT-IR spectrophotometer. ¹H-NMR spectra were obtained at 400.13 MHz, on a Bruker Avance 400 DPX spectrometer. Electron-Spray Ionization (ESI) mass spectra were obtained on a Micromass-Platforn LC spectrometer for solutions of the measured compounds in MeOH. Microanalyses were performed on a Carlo Erba EA 1108 Elemental Analyzer. All new compounds gave satisfactory microanalytical data to within ±0.3 of the calculated values. Flash Column Chromatography (FCC) was performed on Merck silica gel 60 (230-400 mesh) and Thin layer Chromatography (TLC) on Merck silica gel F₂₅₄ films (0.2 mm) precoated on aluminium foil. The solvent or solvent systems used were : (A) PhMe/EtOAc (95:5), (B) PhMe/EtOAc (9:1), (C) PhMe/EtOAc (7:3), (D) PhMe/EtOAc (1:1), (E) CH₂Cl₂/MeOH (9:1), (F) CHCl₃/MeOH (9:1), (G) CHCl₃/MeOH/conc. NH₃ (7:3:0.3), (I) CHCl₃/MeOH/conc. NH₃ (6:4:0.4), (J) CHCl₃/MeOH/conc. NH₃ (5:5:0.5). Spots were visualized with UV light at 254 nm and ninhydrin. All solvents used were dried according to standard procedures prior to use. Experiments involving retinoids were routinely conducted under an atmosphere of Ar and with protection from light. Drying of solutions was effected with anhydrous Na₂SO₄, whereas evaporation of the solvents was performed under reduced pressure in a rotary evaporator at a bath temperature not exceeding 40° C.

The examples below are given so as to illustrate the practice of this invention. They are not intended to limit or define the entire scope of the invention.

Example 1 Preparation of Succinimidyl Retinoate (21 a)

To an ice-cold solution of all-trans-retinoic acid (5) (3.00 g, 10 mmol) in dry THF or DMF (30 ml) was added sequentially HOSu (1.72 g, 15 mmol) and DCC (2.48 g, 12 mmol) and the resulting mixture was stirred for an additional 30 min at 0° C. and for overnight at ambient temperature. The precipitated DCU was filtered off and washed several times with EtOAc. The combined filtrates were washed sequentially with an ice-cold 5% aqueous (aq.) NaHCO₃ solution, H₂O and twice with brine. Drying, followed by filtration and evaporation of the solvent left a residue. FCC of the residue using as eluant the solvent system A, pooling the fractions containing pure product, evaporation and trituration with Et₂O gave 3.38 g (85%) of yellowish crystalline ester 21 a following overnight refrigeration. R_(f)(A) : 0.24. M.p. : 173-76° C. FT-IR (cm⁻¹) : 1758, 1732, 1626, 1595, 1574, 1558. 400 MHz ¹H-NMR (CDCl₃) : δ 7.152 (1H, dd, J 11.6 and 15.2 Hz, H-6), 6.352 (2H, d, J 15.2 Hz, H-5 and H-11), 6.176 (1H, d, J 16.0 Hz, H-10), 6.166 (1H, d, J 10.3 Hz, H-7), 5.954 (1H, s, H-2), 2.852 (4H, br. S, H-2′ and H-3′), 2.382 (3H, s, H-4), 2.030 (3H, s, H-9), 2.030 (2H, m, H-14), 1.722 (3H, s, H-20), 1.613 (2H, m, H-15), 1.472 (2H, m, H-16), 1.035 (6H, s, H-18 and H-19) ppm. Elemental analysis based on C₂₄H₃₁NO₄ ((Calc.)

Found) : C, (72.52) 72.69; H, (7.86) 7.72; N, (3.52) 3.28.

Example 2 Preparation of N¹,N¹²-Bisretinoylspermine (3DIa)

Direct Method A:

To an ice-cold solution of spermine (1) (0.55 g, 2.7 mmol) in dry CH₂Cl₂ (25 ml) was added ester 21 a (1.99 g, 5 mmol). The resulting solution was stirred for an additional hour at 0° C. and then placed in the refrigerator for overnight. The precipitated product was filtered off, washed on the filter with ice-cold CH₂Cl₂ and dried under reduced pressure to give 2.02 g (80%) of the bishydroxysuccinimidate salt of 3DIa as a yellow solid.

R_(f)(I) : 0.40 (free base) and 0.13 (HOSu). M.p.: 149-52° C. FT-IR (cm⁻¹) : 3430, 3317, 1674, 1647. ESI-MS (m/z) : 768.74 (MH), 767.75 (M), 485.56 (R¹CO-SPM+H), 580.02 (MH-C₁₄H₂₀), 384.72 (MH₂/2). 400 MHz ¹H-NMR (d₆-DMSO): δ 8.040 (2H, unresolved t, NHCO), 6.912 (2H, dd, J 12.1 and 14.2 Hz, H-6), 6.33-6.15 (8H, m, H-5, H-7, H-10, H-11), 5.840 (2H, s, H-2), 5.780 (4H, s, H₂N⁺), 3.150 (4H, unresolved q, H-1′), 2.529 (16H, m, H-3′, H-4′, H-2″, H-3″), 2.290 (6H, s, H-4), 2.024 (4H, unresolved t, H-14), 1.976 (6H, s, H-9), 1.704 (6H, s, H-20), 1.598 (8H, m, H-15, H-2′), 1.474 (8H, m, H-16, H-5′), 1.032 (12H, s, H-18, H-19) ppm. Elemental analysis based on C₅₈H₈₈N₆O₈ ((Calc.) Found) : C, (69.85) 69.56; H, (8.89) 8.97; N, (8.43) 8.62.

Direct Method B:

When CHCl₃ was used as the reaction solvent, complete solution of reactants and products was observed. The reaction was found complete (by TLC) within 30 min at 0° C. and then it was worked-up by diluting the resulting solution with EtOAc, washing sequentially twice with a 5% aq. NaHCO₃ solution and twice with water. The organic phase was then dried and evaporated to leave crude product, which was purified by FCC using as eluant the solvent system I to give pure free 3DIa, as a yellow powder, in 75% yield.

Alternatively and in order to facilitate the work-up and purification by FCC procedures, after the diacylation of spermine, in situ protection of the remaining free secondary amino functions with the trifluoroacetyl(Tfa) group, by treating the reaction mixture with trifluoroacetic anhydride (Tfa₂O) in the presence of Et₃N for 5 min at 0° C. και for 30 min at ambient temperature, takes place. Then, the fully protected product is subjected initially to purification with FCC and finally to removal of the temporary protecting groups by treating with K₂CO₃ at refluxing MeOH/H₂O (6:0.5) for 30 min, giving the free product 3DIa in 68% total yield.

Indirect Method:

To an ice-cold solution of N¹,N¹²-Trt₂-SPM (22 a; n=1) (2 g, 3 mmol) in dry CH₂Cl₂ (30 ml) was added sequentially ^(i)Pr₂NEt (1.4 ml, 8 mmol) and Fmoc-OSu (2.2 g, 8 mmol). After 30 min at ambient temperature, the reaction mixture was diluted with CH₂Cl₂ (100 ml) and washed sequentially twice with a 5% aq. NaHCO₃ solution and twice with water. Drying and evaporation of the solvent left a residue which was subjected to FCC using as eluant the solvent system B to give 3.26 g of pure product N⁴,N⁹-Fmoc₂-N¹,N¹²-Trt₂-SPM as a foam. This was then treated with a solution (20 ml) of trifluoroacetic acid (TFA) in CH₂Cl₂ (1:4) for 30 min at 0° C. Evaporation of the solvent left a residue which was triturated with Et₂O/hexane (1:1) and refrigerated overnight. The supernatant liquid was poured off and the residue was subjected to FCC using as eluant the solvent system E to give 1.8 g (69% yield based on 22 a) of the bistrifluoroacetate salt of N⁴,N⁹-Fmoc₂ -SPM (23 a) as a foam.

To an ice-cold solution of 23 a (0.88 g, 1 mmol) in 2 ml DMF/CHCl₃ (1:1) was added sequentially ^(i)Pr₂NEt (0.7 ml, 4 mmol) and ‘active’ ester 21 a (0.79 g, 2 mmol). After 1 h at ambient temperature, the reaction mixture was diluted with 50 ml EtOAc and washed once with a 5% aq. NaHCO₃ solution and twice with water. Drying, evaporation and FCC with the eluant D gave the intermediate 24 a. This was then treated with a solution (10 ml) of piperidine (Pip) in CH₂Cl₂ (1:4) for 15 min at ambient temperature. Evaporation of the solvent, trituration of the residue with Et₂O, refrigeration and finally filtration gave 0.57 g (74%) of 3DIa.

Example 3 Preparation of N¹-retinoylspermine (3DIIa)

To an ice-cold solution of 23 a (0.88 g, 1 mmol) in 2 ml DMF/CHCl₃ (1:1) was added ^(i)Pr₂NEt (0.4 ml, 2.3 mmol) and then ‘active’ ester 21 a (0.32 g, 0.8 mmol) in small portions within 1 h. After additional 30 min at ambient temperature, the reaction mixture was diluted with 50 ml EtOAc and washed once with a 5% aq. NaHCO₃ solution and twice with water. Drying, evaporation and FCC of the residue with the eluant F gave the intermediate 25 a with R_(f)(F) 0.15. This was then treated with a solution (10 ml) of Pip in CH₂Cl₂ (1:4) for 30 min at ambient temperature. Evaporation of the solvent under reduced pressure, trituration of the residue with Et₂O and refrigeration gave a precipitate. Finally, filtration and evaporation of the filtrate gave 0.18 g (47%) of 3DIIa as a yellowish foam. ESI-MS (m/z) : 485.86 (MH).

It should be noted that in the above described reaction of compound 23 a with ester 21 a, considerable amounts of the corresponding diacylated spermine were also formed, but this by-product is easily separated from the monoacylated spermine derivative 25 a, during the afore mentioned FCC. The trishydrochloride salt of 3DIIa was also obtained, as a yellowish powder, by triturating an ice-cold solution of the free base in MeOH with an ice-cold solution of 1.2 N solution of gaseous HCI in anhydrous MeOH, followed by immediate precipitation of the thus formed salt with Et₂O.

Example 4 Preparation of N⁴,N⁹-Bis(All-Trans-Retinoyl)Spermine (3DIIIa)

To an ice-cold solution of the bistrifluoroacetate salt of N¹,N¹²-bistrifluoroacetylspennine (0.32 g, 0.5 mmol) in anhydrous CHCl₃ (1 ml) was added ^(i)Pr₂NEt (0.7 ml, 4 mmol) and a mixture consisted of all-trans-retinoic acid (0.3 g, 1 mmol) and PyBrOP (0.6 g, 1.28 mmol) in small portions over a period of 1 h. After 30 min at ambient temperature, the reaction mixture was diluted with CHCl₃ and washed sequentially with an ice-cold 5% aq. NaHCO₃ solution (twice) and water (twice). Drying and evaporation left a residue from which pure intermediate 28 a (R=R¹) was obtained through FCC using the solvent system D as eluant. Intermediate 28 a was dissolved in 4 ml MeOH and treated with 0.4 ml of a 4.75 N aq. NaOH solution for 2 h at ambient temperature. MeOH was then removed under reduced pressure and the residue was taken up in 20 ml water and extracted twice with CH₂Cl₂. The combined organic layers were washed twice with brine, dried and evaporated to leave 0.16 g (40%) of pure 3DIIIa as a yellow powder. R_(f)(J): 0.26. FT-IR (cm⁻¹): 3434, 1620. ESI-MS (m/z) : 790.30 (ANa), 768.31 (MH). Elemental analysis based on C₅₈H₈₈N₆O₈ ((Calc.) Found) : C, (69.85) 70.08; H, (8.89) 8.60; N, (8.43) 8.21.

Example 5 Preparation of N⁴-Acitretinoylspermidine (3DVIb)

A solution of spermidine (2) (0.73 g, 5 mmol) and ethyl trifluoroacetate (2 ml, 17,5 mmol) in acetonitrile (15 ml) containing 0.11 ml (6 mmol) H₂O was refluxed for overnight and then the solvent evaporated to leave 2.1 g (92% yield) of the monotrifluoroacetate salt of N¹,N⁸-bistrifluoroacetylspermidine as a foam, which was used as such into the next step. Thus, to an ice-cold solution of this salt (0.50 g, 1.1 mmol) in anhydrous DMF (1.4 ml) and CHCl₃ (1 ml) was added ^(i)Pr₂NEt (0.7 ml, 4 mmol) followed by acitretinoin (0.34 g, 1.06 mmol) and PyBrOP (0.82 g, 1.76 mmol). The reaction mixture was stirred at 0° C. for 30 min and at ambient temperature for overnight. Then diluted with EtOAc and washed once with an ice-cold 5% aq. NaHCO₃ solution and twice with cold H₂O, dried and evaporated to leave a residue. From this residue, 0.60 g (86%) of the fully protected 3DVIb was obtained as a yellow oil after FCC purification using as eluant the solvent system D. R_(f)(D) 0.26. The product had ESI-MS (rn/z): 668.23 (MNa), 645.92 (MH). Fully protected 3DVIb (0.60 g, 1 mmol) was dissolved in MeOH (60 ml) and H₂O (6 ml) and K₂CO₃ (0.52 g, 4 mmol) were added and the resulting mixture was refluxed for 90 min. Then filtered hot and concentrated to dryness. The residue was subjected to FCC, using the solvent system G as eluant, and the fractions with R_(f)(G) 0.12 were pooled and evaporated to leave pure product 3DVIb (0.38 g, 83%) as a yellowish foam. The product had ESI-MS: 454.33 (MH).

Example 6 Preparation of N⁸-Acitretinoylspermidine (3DVIIb)

To an ice-cold solution of N⁸-Trt-SPD (30) (0.5 g, 1.3 mmol) was added ^(i)Pr₂NEt (0.5 ml, 2.6 mmol) and Fmoc-OSu (0.5 g, 2.6 mmol). After 30 min at 0° C., the reaction mixture was diluted with EtOAc and washed once with an ice-cold 5% aq. NaHCO₃ solution, then H₂O and finally brine and dried. Filtration, evaporation and FCC of the residue using the solvent system B as the eluant, gave pure product which was immediately treated with 10 ml of a solution of TFA in CH₂Cl₂ (3:7) for 30 min at 0° C. Solvent evaporation, trituration of the residue with Et₂O and rejection of the supernatant liquid left 0.41 g (45% yield) of the trifluoroacetate salt of N¹,N⁴-Fmoc₂-SPD. R_(f)(E) 0.21. ESI-MS (m/z): 704.64 (MH).

To an ice-cold solution of this salt (0.34 g, 0.48 mmol) in DMF (2 ml) was added ^(i)Pr₂NEt (0.2 ml, 1.2 mmol) and the ‘active’ ester 21 b (0.2 g, 0.48 mmol). After 1 h at 0° C. and 1 h at ambient temperature, the reaction mixture was diluted with EtOAc and washed twice with an ice-cold 5% aq. NaHCO₃ solution and twice with H₂O, dried and evaporated to dryness. The residue was subjected to FCC, using as eluant the solvent system C to give 0.31 g (72% yield) of the fully protected 3DVIIb as a yellowish foam. R_(f)(B) 0.27. ESI-MS (m/z) : 899.08 (MH). This intermediate (0.3 g, 0.33 mmol) was subsequently treated with a 20% solution of Pip in CH₂Cl₂ for 2 h at ambient temperature. The solvent was then evaporated and the residue was triturated with Et₂O. The supernatant liquor was discarded and this procedure was repeated. Finally, drying of the residue left 0.14 g (93%) of pure product 3DVIIb as a yellow foam. ESI-MS (m/z): 455.02 (MH).

Example 7 Biological Evaluation of Compounds as RNase P Inhibitors

RNase P assays were carried out at 37° C. in 20 μbuffer D (50 mM Tris/HCl pH 7.6, 10 mM NH₄Cl, 5 mM MgCl₂ and 5 mM dithiothreitol) if RNase P isolated from D. discoideum was used (Stathopoulos et al.; EUR. J. BIOCHEM. 228, 976 (1995)) or buffer K (50 mM Tris/HCl pH 7.5, 100 mM NH₄Cl, 5 mM MgCl₂ and 5 mM dithiothreitol) if RNase P isolated from human epidermal keratinocytes was used (Drainas et al, unpublished data), containing 2-5 finol pre-tRNA^(ser) substrate (an in vitro labeled transcript of the Schizosaccharoinyces pombe tRNA^(ser) gene supSI) and 1.3 μg protein from the RNase P fraction. Stock solutions of retinoids (natural or synthetic), are prepared in 100% dimethylosulfoxide (DMSO). When retinoids are used, enzyme assays are carried out in the presence of 10% DMSO. The reactions were stopped by addition of 5 μl stop dye (80% formamide, 50 mM EDTA, 0.1% bromophenol blue, 0.1% xylene cyanol). Reaction products were resolved on a denaturing 10% polyacrylamide/8 M urea gel and visualized by autoradiography without drying. Activity was quantified by Cerenkov counting of excised gel slices.

Example 8 Biological Evaluation of Compounds as Anti-Inflammatory Agents

For the purpose of the study, peripheral blood mononuclear cells (PBMC) from ten healthy volunteers (age 33-52 yrs) were incubated in 1 ml volume (RPMI 1640/10% FCS) for varying time periods at 37° C. in a CO₂ (5%) incubator in the presence or absence of PMA (Sigma, St Louis, Mo.), ionomycin (Sigma, St Louis, Mo.) and/or the polyamine-retinoid conjugate (10⁻⁴, 10⁻⁵, 10⁻⁶ M) as well as a protein transport inhibitor, brefeldin (Sigma, St Louis, Mo.) to prevent cytokine secretion in the extracellular space.

Following this incubation, PBMC were stained with either an anti-CD4-FITC or anti-CD8-FITC monoclonal antibody (Beckton Dikinson Hellas, Athens, Greece) in a PBS buffer containing 0.5% BSA and 0.01% NaN₃, and were subsequently fixed with paraformaldehyde and incubated overnight. In the next step, fixed PBMCs were washed and resuspended in a PBS buffer containing 0.5% BSA, 0.5% saponin (Sigma, St Louis, Mo.) (to permeabilize cells) and 0.01% NaN₃. Fixed PBMC were subsequently stained with an anti-IL-2/PE or anti-IFN-γ/PE monoclonal antibody (Diaclone, Besancon, France) and analysed for intracellular expression of IL-2 or IFN-γ and membrane expression of the CD4 or CD8 antigens in a FACSCAN flow cytometer. Throughout this step, saponin-supplied PBS was used, since its permeabilisation effect is reversible. The immunofluorescence cut-off was set up in unstimulated cultures as background and results were expressed either as the percentage of CD4/IL-2+ and CD8/IL-2+ (FIG. 9) and CD8/IFN-γ⁺ and CD4/IFN-γ⁺ (FIG. 11) cells, or alternatively as their mean fluorescence intensity (FIGS. 10 and 12, respectively).

It is to be understood that, while the foregoing invention has been described in detail by way of illustration and example, numerous modifications, substitutions and alterations are possible without departing from the spirit and scope of the invention as described in the following claims. 

1. One or more conjugate of a polyamine with an acidic retinoid, in which an R group in a) and/or b) below is one of the retinoid residues R¹-R⁶ set forth in the following acidic retinoids, the retinoid residues obtained by removing the COOH group from each of the following acidic retinoids:

and said polyamine is: a) a linear polyamine, in which case the one or more conjugate has the following formulae:

 wherein n is 1 to 9; or b) a branched polyamine, in which case the one or more conjugate has the following formula:

wherein R′ is COR or (CH₂)₃NHCOR and R″ is COR or (CH₂)₃NHCOR and n is one of the numbers 1, 2 or
 7. 2. A method for the preparation of the one or more conjugate according to claim 1 involving initially step a), followed by step b) or step c): a) synthesis of a compound with the formula

 wherein R is one of the retinoid residues R¹-R⁶ of claim 1, which involves esterification of an acidic retinoid with N-hydroxysuccinimide (HOSu) in the presence of a coupling agent, which is N,N′-dicyclohexylcarbodiimide (DCC) and purification with flash column chromatography to obtain a purified succinimidyl ester; b) direct selective acylation of the primary amino functions of the polyamine with the purified succinimidyl ester; or c) selective acylation of the secondary amino functions of the polyamine, protected at its primary amino functions with a trifluoroacetyl group or a 9-fluorenylmethoxycarbonyl group, with the acidic retinoid of claim 1 in the presence of a coupling agent, which is bromotripyrrolidinophosphonium hexafluorophosphate (PyBrOP), followed by deprotection.
 3. A method according to claim 2, which method involves the direct selective acylation of the primary amino functions of the polyamine or its corresponding hydrochloride or trifluoroacetate salts with the compound of the step a) of claim 2, wherein a solvent is used which is selected from dichloromethane, chloroform and dimethylformamide.
 4. A method according to claim 3 wherein the selective acylation of the primary amino functions of the polyamine is carried out with any other activated carboxylic acid derivative known to acylate selectively primary amino functions in the presence of secondary amino functions.
 5. A method according to claim 2 wherein selective mono- or bis-acylation of the primary amino functions of the polyamine takes place indirectly and involves the following steps: (i) protection of the secondary amino functions of the polyamine, bearing the trityl protecting group at its primary amino functions, with the 9-fluorenylmethoxycarbonyl group or the trifluoroacetyl group; (ii) detritylation; (iii) mono- or bis-acylation with the compound of step a) of claim
 2. 6. A method according to claim 2 wherein the selective acylation of the secondary amino functions of the polyamine involves the following steps: (i) selective trifluoroacetylation of the primary amino functions of the polyamine; (ii) acylation of the secondary amino functions with the acidic retinoids in the presence of the coupling agent PyBroP; (iii) removal of the trifluoroacetyl groups by alkaline hydrolysis.
 7. A pharmaceutical preparation or product containing the one or more conjugate claimed in claim 1 and a pharmaceutically acceptable carrier.
 8. A method according to claim 3, wherein a base is used which is triethylamine or diisopropylethylamine.
 9. A method according to claim 5, which further involves the following step: (iv) complete deprotection and purification by flash column chromatography. 